In recent years, body fat mass is gaining attention as an indicator used to determine the health of a measurement subject. In particular, visceral fat mass is gaining attention as an indicator for determining whether or not a person is suffering from central obesity. Central obesity is said to bring about lifestyle-related diseases that can easily lead to artery hardening, such as diabetes, hypertension, and hyperlipidemia, and the stated indicators hold promise in terms of preventing such diseases. “Visceral fat” refers to fat that accumulates around the internal organs on the inner side of the abdominal muscles and the back muscles, and is distinct from the subcutaneous fat that is located toward the surface of the trunk area. It is typical to employ the area occupied by visceral fat in a cross-section of the trunk area that corresponds to the navel (referred to as a “visceral fat cross-sectional area” hereinafter) as an indicator of the visceral fat mass.
Normally, visceral fat mass is measured by analyzing images obtained through X-ray computed tomography (CT), magnetic resonance imaging (MRI), or the like. In such image analysis, the visceral fat cross-sectional area is calculated geometrically from a tomographic image of the trunk area obtained by using X-ray CT, MRI, or the like. However, it is necessary to use several pieces of large equipment installed in a medical facility, such as X-ray CT, MRI, or other machines, in order to make use of such a measurement method; thus it is extremely difficult to measure visceral fat mass on a daily basis through such a measurement method. X-ray CT also poses the problem of exposure to radiation, and thus cannot necessarily be called a desirable measurement method.
A body impedance technique is being considered as an alternative to these measurement methods. The body impedance technique is a method for measuring body fat mass widely used in household-based body fat measurement devices; in this technique, electrodes are placed in contact with the four limbs, the body impedance is measured using those electrodes, and the body fat mass is calculated from the measured body impedance. The stated household body fat measurement device makes it possible to accurately measure the extent of body fat buildup throughout the entire body or in specific areas such as the four limbs, the trunk area, or the like.
However, conventional body fat measurement devices that use the body impedance technique measure the extent of body fat buildup throughout the entire body or in specific areas such as the four limbs, the trunk area, or the like, as mentioned earlier, and are not capable of accurately extracting and measuring the extent of visceral fat buildup, the extent of subcutaneous fat buildup, and the like individually. This is because, as mentioned above, conventional body fat measurement devices are configured so that the electrodes are attached only to the four limbs, and thus the visceral fat and subcutaneous fat cannot be accurately measured individually.
Accordingly, bringing electrodes into direct contact with the trunk area, measuring the body impedance using those electrodes, and individually and accurately calculating the visceral fat mass and the subcutaneous fat mass based on that measurement is being considered as a way to solve this problem.
For example, JP 2002-369806A (Patent Literature 1) discloses a body fat measurement device configured so that electrodes are provided on the inner circumferential surface of a belt member and the belt member is wrapped around and anchored to the trunk area of a measurement subject, thus placing the electrodes in contact with the trunk area.
Meanwhile, JP 2005-288023A (Patent Literature 2), JP 2008-23232A (Patent Literature 3), JP 2008-237571A (Patent Literature 4), and so on disclose body fat measurement devices configured so that electrodes are provided on the surface of a fitting unit that is fitted to the abdominal area of a measurement subject and the fitting unit is pressed against the abdominal area, thus placing the electrodes in contact with the abdominal area.
Furthermore, JP 2007-14664A (Patent Literature 5) discloses a body fat measurement device configured so that the device is divided into a fitting unit that is fitted to the abdominal area of a measurement subject and a platform unit for the measurement subject to stand upon, where abdominal area electrodes are provided on the surface of the fitting unit, hand electrodes are provided on a handle portion of the fitting unit, and foot electrodes are provided on the stated platform unit; the hand electrodes are placed in contact with the measurement subject's palms by the measurement subject gripping the handle portion of the fitting unit, the abdominal area electrodes are placed in contact with the abdominal area by the measurement subject pressing the fitting unit against his or her abdominal area using the hands that grip the handle portion, and the foot electrodes are placed in contact with the soles of the measurement subject's feet by the measurement subject standing upon the platform unit.
In addition, although not discussing a specific device configuration, JP 2008-228890A (Patent Literature 6) mentions being able to accurately measure visceral fat mass and subcutaneous fat mass by placing electrodes in contact with the back of a measurement subject's trunk area (that is, the back) without placing electrodes in contact with the measurement subject's abdominal area and placing electrodes in contact with the hands and feet of the measurement subject, measuring the body impedance, and calculating the visceral fat mass and the subcutaneous fat mass based on the measured body impedance. One of the reasons for this is that the subcutaneous fat that accumulates on the abdominal area side is relatively thinner than the subcutaneous fat that accumulates on the back area side, and thus if the electrodes are placed in contact with the abdominal area, the current that is applied will flow through fat-free areas, which makes it easy for errors to occur.
Meanwhile, to make it possible to measure the visceral fat mass, subcutaneous fat mass, and so on with a high degree of accuracy using the stated body impedance, it is necessary to take actual measurements of the measurement subject's body build, such as the circumferential length of the trunk area, the trunk area width, and the trunk area depth, and use the measurements in computation processes for calculating the body fat mass.
For example, according to the body fat measurement device disclosed in the stated JP 2005-288023A, a fitting unit that is fitted to a measurement subject's abdominal area is provided upon a pair of arm portions, which make contact with both sides of the measurement subject's trunk area (in other words, both flanks), so that the fitting unit is mobile; the trunk area width is measured by bringing the arm portions into contact with both flanks, and the result of that actual measurement is used in computation processes for calculating body fat mass.
In addition, according to the body fat measurement device disclosed in the stated JP 2008-23232A, a fitting unit that is fitted to a measurement subject's abdominal area is provided upon an arm portion, which makes contact with the measurement subject's back, so that the fitting unit is mobile; the trunk area depth is measured by bringing the arm portion into contact with the back, and the result of that actual measurement is used in computation processes for calculating body fat mass.
Furthermore, according to the body fat measurement device disclosed in the stated JP 2008-237571A, a trunk area width measurement unit disposed at a distance from the outside of both sides of the measurement subject's trunk area is configured separate from a fitting unit that is fitted to the measurement subject's abdominal area, and multiple non-contact range sensors are provided in the trunk area width measurement unit so as to take an actual measurement of the trunk area width; the result of that actual measurement is used in computation processes for calculating body fat mass.
Furthermore, although the technique does not bring electrodes into contact with a measurement subject's trunk area, JP 2009-22482A (Patent Literature 7) discloses a body fat measurement device in which foot electrodes are provided on a platform unit onto which the measurement subject steps, a trunk area width measurement unit disposed at a distance from the outside of both sides of the measurement subject's trunk area is supported on a support column portion that extends upward from the stated platform unit while the measurement subject stands on the platform unit, and multiple non-contact range sensors are provided in the trunk area width measurement unit so as to take an actual measurement of the trunk area width; the result of that actual measurement is used in computation processes for calculating body fat mass.